Exhaust gases containing hydrogen from facilities and plants such as semiconductor manufacturing facilities and chemical plants are generally disposed of by burning at high temperatures in incinerators. FIG. 5 shows a typical prior art high-temperature combustion disposal apparatus used in semiconductor manufacturing facilities. In this apparatus, exhaust gas A containing hydrogen from semiconductor manufacturing line B, which includes a hydrogen annealing furnace, is first led into a quartz furnace 50 containing an ignition silicon chip 52 which is heated by a heating lamp 53. Hydrogen in the exhaust gas A gushing out of a nozzle 51 is then subject to complete combustion at approximately 1800 to 2000.degree. C. in the quartz furnace 50.
Quartz furnace 50 has another pipe 54 connected thereto. Oxygen is fed into the quartz furnace 50 through the pipe 54 to assist in complete combustion of the hydrogen. In order to ensure complete combustion of the hydrogen and to ensure safety, the amount of oxygen to be fed into the furnace is set at more than half of the amount of hydrogen.
In treatment of exhaust gases containing hydrogen by an external combustion unit C as shown in FIG. 5, the exhaust gas A can be burned completely with high efficiency in a relatively small external combustion unit C, provided that the exhaust gas A containing hydrogen flows from the semiconductor manufacturing line B at a nearly fixed rate and that the concentration of hydrogen in the exhaust gas A does not fluctuate too much. However, the disposal technique employing the aforesaid external combustion unit C has a fundamental drawback in that unstable combustion due to fluctuations in the discharge amount of exhaust gas A or changes in the concentration of hydrogen in the exhaust gas A could result in an explosion of the external combustion unit C.
If, for instance, the flow rate of exhaust gas A containing hydrogen from the semiconductor manufacturing line decreases, with the level of hydrogen dropping and staying at almost nil longer than a specific time, then the combustion flame near the tip of the nozzle 51 will go out, with the temperature dropping near the tip of the nozzle 51. Unless ignition silicon chip 52 is heated again, combustion will not be resumed, even when the flow rate of the exhaust gas A and the concentration of hydrogen rise again. Hydrogen-containing gas A would then be discharged untreated out of the combustion unit C, bringing about a very dangerous situation.
Another problem is that if the discharge rate of exhaust gas A drops substantially, backfire may spread toward the semiconductor manufacturing line B from the external combustion unit C through the pipe line 55. In this circumstance, there will arise a danger of explosion of the semiconductor manufacturing line B itself.
To ensure safety, the prior art combustion unit C is equipped as a matter of course with various safety measures. The safety measures include an alarm, an automatic igniter, and an automatic gas shutoff device that will work when the combustion flame of the mixed gas from nozzle 51 goes out. But if those safety measures are actuated each time the combustion flame in the external combustion unit C goes out or the combustion becomes unstable, operation of the semiconductor manufacturing line B will be affected, which can have an adverse effect on the quality of semiconductor products.
In another environment, at nuclear power stations, when the reactor coolant water is decomposed by radiation, a hydrogen-oxygen mixture is generated in the coolant water. This hydrogen-oxygen mixture is recombined using a catalyst. The principle of that recombination technique as disclosed in unexamined Japanese patent application 57-049895 is this, with reference to FIG. 6: The hydrogen-oxygen mixture A separated by an air extractor D from coolant water E is first mixed with a large quantity of steam S to produce a mixture A.sub.0 whose concentration of hydrogen is below the explosion limit. This mixture A.sub.0 is then led to a recombiner 60 including a catalyst unit 61 provided therein through an upper nozzle 62 where hydrogen and oxygen are recombined into steam through catalytic action at a specific high temperature. The steam thus produced is then discharged through a lower nozzle 63.
However, the technique outlined in FIG. 6 is for the treatment of large quantities of a mixture fluid A.sub.0 mixed with large quantities of steam S. The recombiner 60 becomes so large in size that it is difficult to install in semiconductor manufacturing facilities. In addition, because the rate of reaction between hydrogen and oxygen in the recombiner 60 is relatively low, unreacted hydrogen is discharged out of recombiner 60 through lower nozzle 63. A complete treatment of the unreacted hydrogen discharged from recombiner 60 in turn requires a separate external combustion unit, which means additional and substantial investment in equipment.